server: Fix regression in partial message handling

If a partial message is flushed into the input pipe for CMake Server,
the parser will try and parse it as a full message because of some bad
loop checks.  This was introduced accidentally in commit
v3.10.0-rc1~365^2~2 (server: Refactor to make the event loop owned by
server object, 2017-03-24).
1 file changed